The present invention relates to a burner-heat exchanger assembly for an external combustion engine, in particular for a Stirling engine or for a Rankine cycle engine. As is known, Stirling engines implement the so-called Stirling cycle to convert thermal energy (in particular a thermal gradient) into work (in particular a cyclic kinematic movement) or vice versa by means of a closed cycle using a gas as thermodynamic fluid, usually air or nitrogen, or helium or hydrogen in the high performance versions. When a suitable difference in temperature is reached between a hot point and a cold point of the Stirling cycle, a cyclic pulsation is triggered, which is usually transformed into reciprocating motion of kinematic members, e.g. pistons or membranes. The pulsation lasts as long as the difference in temperature is maintained by administering heat to the hot point and subtracting heat from the cold point.
An alternative to Stirling engines are Rankine engines which implement the so-called Rankine cycle to convert thermal energy into work (in particular a cyclic kinematic movement) by means of an endoreversible thermodynamic cycle consisting of two adiabatic transformations and two isobar transformations.
The burners used as heat source for external combustion engines must provide the quantity of heat required by the thermodynamic cycle, have a size and shape such as to promote an efficient and quick heat exchange between the combustion gases and the thermodynamic fluid, adapt to the space conditions of the engine, avoid an undesired overheating of the components of the engine itself, resist high temperatures and possible “heat accumulations”, resist mechanical stresses due to thermal expansions and the mechanical stresses, e.g. vibrations, due to the cyclical movement of the pistons of the external combustion engine.
The burner and heat exchanger assembly should promote the most efficient heat exchange possible in order to allow the external combustion engine to reach increased levels of energy efficiency.
Although they are satisfactory with reference to certain specific needs, burner-heat exchanger assemblies of the known art are not capable of reconciling the entirety of all the needs listed above in an optimal manner, in particular with reference to a quick and efficient heat exchange and to the thermal and/or mechanical stresses.
It is therefore the object of the present invention to provide a gas burner-heat exchanger assembly for an external combustion engine having features such as to best reconcile the needs listed above.